Regulations And Control Measures Of Pile Foundation Near Subway Station By Excavation For Shallow Tunnels

There are lots of metropolis high-rise, over bridge which mostly adopt pile foundation. Confined by the tendency of lines and underground space, subway projects inevitably go from the inferior and sides even at position of these pile foundations sometimes. Although there are great progresses about underground construction technology and some have reached to international advance, therefore constructions remain avoidable disturbed soil and bring distortion and displacement which get piles and around soil to occur interactively and create piles' redundant deformation and internal force .It has a bad effect. It research the effect of piles near subway project by Excavation for shallow tunnels and draws up distortion control standards to control deformation of close pile foundations. It ought to ensure pile foundation and bridge safe. All of these become exact puzzle pressing in engineering construction for solution. The text incorporated under constructing Peking subway number 10—Guomao station engineering to study aiming at the above question. The paper's primary content and result as follows.1.The thesis research mostly rule and influencing factor in zone affected around subway project by Excavation for shallow tunnels. The geologic strata transform alongwith the construction carrying on is divided into three blocks-----prophase settlement area,quick settlement area and settlement convergence area and four stages with in advance settlement, rapid settlement, sinking to a stability and the long-term slow transformed. The main factors include structure form of station, groundwater and ration between cover and striding and excavating span, the soil's mechanics character and construction method, beforehand protecting measures, excavating length and speed of construction, the form early, the technique parameters and opportune moments of construction, construction method of the secondary lining and rock round and the close extent between elementary lining and the secondary etc. Information-based construction and the dynamic state management are the important means that controlled the settlement. The station structure should follow the principle of connect a rather small span of arch to be apart from, the caves are near not connected, adopting to separated type station much, Excavation influence for the surround geologic strata and the environment. It research and analyzes characteristics of geologic strata's settlement in Guomao station and thinks the cave-pile method stake a method to get the ruler that settlement of lengthways is obviously divided into declining quickly area, sharp declining area and declining convergence area. But the sharp decline area is classified into three stages, namely decline stage of small holes construction which shares 30-40% of decline the quantity, the decline stage of supporting arch which shares 25-35% of decline the quantity and the decline stage of the lower part soil escavated which shares 25-30% of decline the quantity. Transverse declines match the PECK curve, which influence 3-4 times of hole's diameter.2.The paper analyzes the position on cross section between the pile foundation and the station structure and adopts an extreme limit equilibrium method to research loads delivery and stabilization of the single pile and pile foundation constructing and gets the factors that were thought to influence the displacement and deformation of pilefoundation-----The relative space position between piles and station, span and height ofstation, method of construction, condition of geologic strata, length and diameter and shape and the loading method and stiffness of piles and so on. Especially h (the vertical distance from the bottom of pile to the top board) and e (the horizontal distance between pile and structure) have prominent influence of stabilization. First, it puts forward that the position relation between pile foundation and the station is divided into the piles above the station, upside piles, the middle piles and the downside piles; or according to the decline area of the pile foundation of the station it is divided into A,B,C three types. These are two classical methods of near piles. Its close extent is 1,2,3,4 and 5 five Classes and put forward close extent of different close foundations. Then it classifies Guomao station and get the close extent.3.It analyzes the influence of displacement of piles for upright and horizontal deformation of the geologic strata the influence of displacement of piles and adopts numerical method to stimulate the main steps of construction in the 3D dynamic state emulation and gets to the regulation of near piles' deformation on each stage. It concludes the whole process based on the measurement data and gets the regulation of decline of close pile foundations. It is thought that the decline caused by the cave-pile technique is corresponding with the process which is divided into the cave-excavation stage, supporting arch stage and the downside soil's excavation stage. The main influences is its space position, especially the minimum distance between the station structure and pile foundation. Secondly length of pile have close effect. Thirdly, the place of the geologic strata condition where the bottom and body of piles also has certain influence. Seen the decline's influence from each construction stage, the ratio of three stages of the piles' decline upside the station is 4:3:3 and small guide hole has the most effect; the ratio of three stages of the downside piles' decline downside the station is 3:4:3 and show supporting arch has the most effect; the ratio of three stages of the piles' decline side the station is 3:3:4 and show below soil excavation has the most effect. Construction disturbs the horizontal displace very much. The arch construction influences the side deformation mostly and the side deformation is more in side than under the station.4.It put forward 8 pieces basic principles of establishment control standard of the decline of close pile and 3 pieces main control index sign that are the max settlement allowed of the single frusta, allowed different settlement of two frustas along horizontal and lognitudinal bridge. It puts forward the foundation's construction processing of near piles and basic principle of protecting piles and some measures to control the deformation and reinforce under concluding the common method to control deformation of near piles.5. Taking Guomao station in the cave-pile construction in Beijing for example, it divides into four sort, four protection grades, three construction stages to carry on a protection and establish 3-grade decline management grade according to the up structure of near pile foundation and confirms construction and adoption method according to protection grades. With typical model of special grade protection 21-pile bridge pile for example, the paper confirms scheme to control the deformation of near pile foundations and each stage protection measures. And it elaborates synthesized reinforce measures—makes deep-drawn piles from the ground and adopts bar planting technique to extent the pile caps assisted support by T beam and to press thin cement into holes to ensure the safety of near pile foundations.